Approach to postoperative hypotension: Clinical sciences

Postoperative hypotension is one of the most common complications in the immediate period after any operation and is associated with an increased risk of morbidity and mortality. The most common causes of postoperative hypotension are general anesthesia and inadequate fluid resuscitation. Other causes include life-threatening conditions like respiratory failure, hemorrhage, and cardiovascular events.

When assessing a patient with postoperative hypotension, your first step is to perform an ABCDE assessment to determine if the patient is unstable or stable. Remember that all hypotensive patients are considered unstable so your priority is to stabilize their hemodynamic status as quickly as possible. To do this, initiate acute management like stabilizing the airway, providing supplemental oxygen, establishing IV access, continuously monitoring vitals, and consider starting IV fluid resuscitation and vasopressors right away.

After that, obtain a focused history and physical exam. Be sure to get the information about the type of operation performed; when it was performed; the type of anesthesia and medications used; as well as preoperative disease and physiologic state of the patient; and allergies.

Following the ABCDE, first assess for respiratory distress. In particular, you’ll want to look for causes of respiratory distress like tension pneumothorax, pulmonary embolism, or anaphylaxis. These conditions may lead to a decrease in left ventricular filling, which can in turn reduce the cardiac output, ultimately resulting in hypotension.

Now, the patient might have a history of underlying lung disease, sustained thoracic trauma, a thoracic procedure, or prolonged ventilatory support, as well as a complication of central line placement. Additionally, the physical exam might reveal absent lung sounds, jugular venous distension with or without tracheal deviation in addition to tachypnea, hypoxia, tachycardia, and altered mental status. With these findings, you can make a diagnosis of tension pneumothorax.

These patients should immediately be treated with needle decompression and chest tube placement.

Here’s a clinical pearl! Physical exam findings are enough to make your diagnosis of tension pneumothorax, as it can be quickly fatal, so you should never delay the treatment to obtain imaging like ultrasound or chest x-ray. However, if you were to perform them, ultrasound would show absent lung sliding against the rib cage, while a chest x-ray would show a visible visceral pleural edge with absent distal lung markings on the affected side, as well as tracheal deviation and mediastinal shift toward the opposite side.

Moving onto the next cause of respiratory distress. History might reveal a hypercoagulable state, such as cancer, previous or current deep vein thrombosis, immobility, trauma like long bone fractures, or any recent major surgery, such as an orthopedic procedure, emergent obstetric operation, or even plastic surgery like liposuction. On exam, in addition to hypotension, you may find tachycardia, hypoxia, dyspnea, cough, and hemoptysis.

If this is the case, consider pulmonary embolism and order an ABG, ECG, and echocardiogram. ABG will show low PaO2 despite high FiO2, with an elevated alveolar-arterial or A-a gradient indicating ventilation-perfusion or V/Q mismatch, as well as elevated CO2; while ECG can show sinus tachycardia or the S1Q3T3 pattern. On echocardiogram, you can expect to see right heart strain and distended inferior vena cava.

If there’s a large central embolus, it’s called a saddle PE. Finally, once you stabilize the patient, you need to obtain a CT pulmonary angiography, or CTA, which will show a filling defect in the pulmonary vasculature. This confirms the diagnosis of pulmonary embolism.

Here’s a clinical pearl! If your patient remains unstable, you should just make a presumptive PE diagnosis without confirming with CTA, and start treatment right away.

The last of the life-threatening respiratory causes to consider is anaphylaxis. Usually, patients will have a personal or family history of allergies to drugs, latex, or intravenous contrast.

On a physical exam, in addition to hypotension, you might see flushing, lip or tongue swelling, skin rash or hives as well as more serious signs and symptoms like respiratory distress, tachycardia, and altered mental status.

These findings should get you to consider anaphylaxis. Keep in mind here that anaphylaxis is a clinical diagnosis, but there should be special considerations for obtaining ABG and echocardiogram in a patient with postoperative hypotension and respiratory distress. ABG is usually normal, while echocardiogram shows a hypercontractile left ventricle and an underfilled right ventricle reflecting systemic vascular vasodilation of anaphylactic shock.

Before we move on, here’s a clinical pearl! There’s many other causes of postoperative distress that, when severe enough, can ultimately lead to hypotension as well! Two of the most common ones include bronchospasm secondary to general anesthesia, aspiration during intubation or extubation.

Alright, let’s move on to hemorrhagic causes of hypotension, which is one of the most serious postoperative complications. Patients who underwent high risk operations for trauma or cardiovascular disease, emergent surgery while on blood thinners or for obstetric and gynecologic emergencies, surgeries requiring intraoperative transfusions, or patients with liver disease. On physical exam, in addition to hypotension, your patient may have tachycardia and tachypnea, as well as altered mental status. You might see external bleeding around the incision, increasing swelling of the surgical site, and abdominal distension if abdominopelvic surgery was performed.